Conventional metal polymer plain bearings with polymer based sliding surfaces are typically composed of two-layer or three-layer composite bearing structures. Both forms rely on a metal backing to provide rigidity and allow the material to be formed into the appropriate shape, more commonly a cylinder. The metal polymer two-layer bearing materials typically rely on directly-applied or adhered polymers. The design of the three-layered bearing typically rely on an adhesive or porous metallic interlayer to attach the polymer bearing lining to the metal backing. In any case, a critical part of providing the appropriate load bearing and tribological characteristics is the composition of the sliding layer.
Chemically resistant layers, such as those made of polytetrafluoroethylene (PTFE), are widely used in industry to protect sensitive parts of machinery or equipment from the corrosive effects of acids or other chemicals. One such use is in one or two piece pump diaphragms commonly used with air or electrically driven diaphragm pumps. In the two piece diaphragms, an outer PTFE overlay diaphragm is commonly used to protect an inner rubber diaphragm from materials that would cause rapid failure of the rubber part alone. In some other cases, the PTFE provides the sole material of construction of the diaphragm.
EP 0 394 518 A1 describes a multilayer slide bearing material in which the metallic support material preferably consists of cold-rolled steel on which a layer of a copolymer of perfluoro(alkyl vinyl ether) and tetrafluoroethylene has been applied as intermediate layer. A sliding layer composed of a PTFE compound material is in turn applied to the intermediate layer. In this slide bearing material, the intermediate layer has the function of establishing firm adhesion of the sliding layer to the support material. In order firstly to ensure adhesion of the intermediate layer to the support material, the surface of the metallic support material in this known slide bearing material has to be pretreated in a suitable manner by wet chemical means. The best results appear to be achieved by chromating of the surface of the metallic support. However, this process is problematical for a variety of reasons, including environmental issues and others. As such, there is a continued need for improved slide bearings.
Moreover, the performance properties of the sliding layer depend from a variety of factors such as the strength of adhesion to the metal backing and the inherent tribological properties of the sliding layer. In conventional bearings, the friction properties of the sliding layer, absent any post-production lubrication, e.g., grease or oil, depend from the amount of a fluoropolymer and/or a filler present in the sliding layer. The majority of the sliding layer usually comprises a non-fluorinated thermoplastic polymer or curable resin that provides structural integrity of the sliding layer. However, the total amount of friction providing fillers or fluoropolymers does not exceed 30 vol %. For example, US 2009/0052822 discloses extrusion-type bearings, which limits in its embodiments the amount of a fluoropolymer in the sliding layer to 20 vol % and the amount of another filler therein to 8 vol %, totaling the friction providing ingredients in the sliding layer to not more than 28 vol %. As such, there is a need to improve slide bearings by increasing the amount of the friction providing ingredients.
Therefore, it would be advantageous if a bearing composite could be produced that would combine the physical demands of the above described bearing with an improvement of the tribological properties of the sliding layers.